U.S. patent application number 09/985728 was filed with the patent office on 2002-07-11 for wafer applied fluxing and underfill material, and layered electronic assemblies manufactured therewith.
This patent application is currently assigned to Loctite Corporation. Invention is credited to Crane, Lawrence N., Konarski, Mark M., Krug, J. Paul, Tishkoff, Rebecca, Torres-Filho, Afranio, Yaeger, Erin K..
Application Number | 20020089067 09/985728 |
Document ID | / |
Family ID | 22939034 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020089067 |
Kind Code |
A1 |
Crane, Lawrence N. ; et
al. |
July 11, 2002 |
Wafer applied fluxing and underfill material, and layered
electronic assemblies manufactured therewith
Abstract
A flip-chip type integrated circuit chip including a chip die
having electrical contacts arranged in a predetermined pattern and
capable of providing electrical interconnection with a carrier
substrate is provided. The chip die includes a fluxing agent
disposed on a surface of the electrical contacts, and a curable
thermosetting underfill composition distinct from the fluxing agent
and disposed in a flowable form over the chip die. Upon mating of
the chip die with the substrate and heating, the electrical
contacts flow and the thermosetting underfill composition cures,
thus adhering the chip die to the substrate, forming a circuit
assembly.
Inventors: |
Crane, Lawrence N.;
(Brookfield, CT) ; Konarski, Mark M.; (Old
Saybrook, CT) ; Yaeger, Erin K.; (Coventry, CT)
; Torres-Filho, Afranio; (Enfield, CT) ; Krug, J.
Paul; (Middletown, CT) ; Tishkoff, Rebecca;
(Hamden, CT) |
Correspondence
Address: |
WEBB ZIESENHEIM LOGSDON
ORKIN & HANSON, P.C.
700 Koppers Building
436 Seventh Avenue
Pittsburgh
PA
15219-1818
US
|
Assignee: |
Loctite Corporation
|
Family ID: |
22939034 |
Appl. No.: |
09/985728 |
Filed: |
November 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60248419 |
Nov 14, 2000 |
|
|
|
Current U.S.
Class: |
257/778 ;
257/779; 257/780; 257/E21.503; 257/E23.119; 257/E23.134 |
Current CPC
Class: |
H01L 2224/29082
20130101; H01L 2924/01023 20130101; H01L 2924/351 20130101; H01L
2924/01078 20130101; H01L 23/3192 20130101; H01L 2224/32225
20130101; H01L 2924/01013 20130101; H01L 24/29 20130101; H01L
2224/056 20130101; H01L 2924/0101 20130101; H01L 2924/01006
20130101; H01L 2224/73204 20130101; H01L 2224/05573 20130101; H01L
2924/01033 20130101; H01L 2224/16225 20130101; H01L 21/563
20130101; H01L 2924/01005 20130101; H01L 2224/05568 20130101; H01L
2224/83856 20130101; H01L 2924/01027 20130101; H01L 2924/01032
20130101; H01L 2924/0105 20130101; H01L 2924/09701 20130101; H01L
2224/83191 20130101; H01L 2924/01015 20130101; H01L 2224/73104
20130101; H01L 2924/01322 20130101; H01L 2924/01016 20130101; H01L
2924/01049 20130101; H01L 2924/01082 20130101; H01L 23/293
20130101; H01L 24/05 20130101; H01L 2924/01039 20130101; H01L
2924/01075 20130101; H01L 2224/73203 20130101; H01L 2924/14
20130101; H01L 2224/73204 20130101; H01L 2224/16225 20130101; H01L
2224/32225 20130101; H01L 2924/00 20130101; H01L 2924/3512
20130101; H01L 2924/00 20130101; H01L 2924/351 20130101; H01L
2924/00 20130101; H01L 2224/056 20130101; H01L 2924/00014
20130101 |
Class at
Publication: |
257/778 ;
257/780; 257/779 |
International
Class: |
H01L 023/02; H01L
023/48; H01L 023/52 |
Claims
What is claimed is:
1. An integrated circuit chip electrically interconnectable with a
carrier substrate comprising: a) a chip die having electrical
contacts arranged in a predetermined pattern capable of providing
electrical interconnection with electronic circuitry on a surface
of the carrier substrate, said electrical contacts being flowable
upon heating; b) a fluxing agent disposed on a surface of said
electrical contacts at a location capable of providing effective
fluxing activity to said electrical contacts of said chip die and
said electronic circuitry of the carrier substrate when said chip
die is mated with the carrier substrate; and c) a curable
thermosetting underfill composition dispensed in a flowable form
over said chip die about said electrical contacts and distinct from
said fluxing agent, wherein upon mating said chip die with said
carrier substrate to form a mated assembly and upon heating said
mated assembly to a temperature sufficient to render said
electrical contacts flowable, said electrical contacts flow to
provide electrical interconnection between said chip die and said
carrier substrate, and said thermosetting underfill composition
cures, thereby adhering said chip die to said carrier
substrate.
2. An integrated circuit chip as in claim 1, wherein said fluxing
agent is disposed over substantially the entire surface of said
electrical contacts.
3. An integrated circuit chip as in claim 1, wherein at least a
portion of said electrical contacts is exposed from said
thermosetting underfill composition.
4. An integrated circuit chip as in claim 1, wherein said
thermosetting underfill composition comprises a curable component,
a curing agent for promoting cure of said curable component, and
optionally, an inorganic filler component.
5. An integrated circuit chip as in claim 4, wherein said curable
component comprises an epoxy resin.
6. An integrated circuit chip as in claim 5, wherein said epoxy
resin is selected from the group consisting of bisphenol-A-type
epoxy resin; bisphenol-F-type epoxy resin; phenol novalec-type
epoxy resin; cresol novalec-type epoxy resin; polyepoxy compounds
based on aromatic amines and epichlorohydrin; polyglycidyl
derivatives of phenolic compounds; polyglycidyl derivatives of
phenol-formaldehyde novalecs; polyglycidyl adducts of amines,
aminoalcohols and polycarboxylic acids; and combinations
thereof.
7. An integrated circuit chip as in claim 4, wherein said curing
agent is selected from the group consisting of anhydride compounds,
amine compounds, amide compounds, imidazole compounds, and
combinations thereof.
8. An integrated circuit chip as in claim 4, wherein said inorganic
filler component may be selected from the group consisting of
materials constructed of or containing reinforcing silicas,
aluminum oxide, silicon nitride, aluminum nitride, silica-coated
aluminum nitride, boron nitride, and combinations thereof.
9. An integrated circuit chip as in claim 1, wherein said fluxing
agent comprises an organic acid.
10. An integrated circuit chip as in claim 1, wherein said fluxing
agent comprises a material selected from the group consisting of
abietic acid, adipic acid, ascorbic acid, acrylic acid, citric
acid, 2-furoic acid, malic acid, polyacrylic acid, and combinations
thereof.
11. An integrated circuit chip as in claim 1, wherein said fluxing
agent comprises a latent organic acid.
12. An integrated circuit chip as in claim 1, wherein said fluxing
agent comprises a thermally-activatable blocked organic acid.
13. An integrated circuit chip as in claim 1, wherein said fluxing
agent further comprises an epoxy compound capable of drying to form
a film of said fluxing agent on said electrical contacts and
capable of reacting with said thermosetting underfill composition
upon curing of said thermosetting underfill composition.
14. An integrated circuit chip as in claim 1, wherein said chip die
is constructed of material selected from the group consisting of
silicon and germanium.
15. An integrated circuit chip as in claim 1, wherein said chip die
is coated with a material selected from the group consisting of a
polyimide-based material, poly-benzocyclobutane-based material, and
a silicon nitride-based material.
16. An integrated circuit chip as in claim 1, wherein said carrier
substrate is constructed of a material selected from the group
consisting of Al.sub.2O.sub.3, silicon nitride, mullite, polyimide,
glass-reinforced epoxy, acrylonitrile-butadiene-styrene, and
phenolic substrates.
17. An integrated circuit chip as in claim 1, wherein said
electrical contacts comprise solder bumps.
18. An integrated circuit chip as in claim 1, wherein reaction
products of said thermosetting underfill composition are
controllably degradable when exposed to appropriate conditions.
19. An integrated circuit chip as in claim 18, wherein said
thermosetting underfill composition comprises a curable compound
having at least one thermally cleavable linkage, a curing agent for
promoting cure of said curable compound, and optionally, an
inorganic filler component.
20. An integrated circuit chip as in claim 19, wherein said
compound having at least one thermally cleavable linkage is
selected from the group consisting of diepoxides including acyclic
acetal groups and full and partial episulfide equivalents thereof;
diepoxides including secondary carbonyl linkages and full and
partial episulfide equivalents thereof; diepoxides including
tertiary carbonyl linkages and full and partial episulfide
equivalents thereof; diepoxides including an aromatic moiety within
the structure and full and partial episulfide equivalents thereof;
and combinations thereof.
21. An integrated circuit chip as in claim 1, wherein said
thermosetting underfill composition when cured provides a
dielectric layer between said chip die and said carrier
substrate.
22. An integrated circuit chip as in claim 1, wherein said chip die
comprises a packaged integrated circuit, and said electrical
contacts are arranged on said packaged integrated circuit for
providing electrical interconnection with said electronic circuitry
of said carrier substrate.
23. A circuit assembly comprising the assembled product of claim
1.
24. A method for assembling an integrated circuit assembly
comprising: a) providing an integrated circuit chip in accordance
with claim 1; b) mating said integrated circuit chip with a carrier
substrate to form a mated assembly; and c) exposing said mated
assembly to temperature conditions sufficient to promote electrical
interconnection between said integrated circuit chip and said
carrier substrate and to cure said thermosetting underfill
composition, thereby adhering said integrated circuit chip to said
carrier substrate.
25. An integrated circuit chip electrically interconnectable with a
carrier substrate comprising: a) a chip die having electrical
contacts arranged in a predetermined pattern capable of providing
electrical interconnection with electronic circuitry on a surface
of the carrier substrate, said electrical contacts being flowable
upon heating; b) a fluxing agent disposed on a surface of said
electrical contacts at a location capable of providing effective
fluxing activity to said electrical contacts of said chip die and
said electronic circuitry of the carrier substrate when said chip
die is mated with the carrier substrate; c) a first thermosetting
underfill composition dispensed in a flowable form over said chip
die about said electrical contacts and distinct from said fluxing
agent; and d) a second thermosetting underfill composition
dispensed in a flowable form over said first thermosetting
underfill composition about said electrical contacts and distinct
from said first thermosetting underfill composition and said
fluxing agent, wherein upon mating said chip die with said carrier
substrate to form a mated assembly and upon heating said mated
assembly to a temperature sufficient to render said electrical
contacts flowable, said electrical contacts flow to provide
electrical interconnection between said chip die and said carrier
substrate, and said first and second thermosetting underfill
compositions are cured, thereby adhering said chip die to said
carrier substrate.
26. An integrated circuit chip as in claim 25, wherein said fluxing
agent is disposed over substantially the entire surface of said
electrical contacts.
27. An integrated circuit chip as in claim 25, wherein at least a
portion of said electrical contacts is exposed from said first and
said second thermosetting compositions.
28. An integrated circuit chip as in claim 25, wherein said first
and said second thermosetting compositions comprise a curable
component, a curing agent for promoting cure of said curable
component, and optionally, an inorganic filler component.
29. An integrated circuit chip as in claim 28, wherein said curable
component comprises an epoxy resin.
30. An integrated circuit chip as in claim 29, wherein said epoxy
resin is selected from the group consisting of bisphenol-A-type
epoxy resin, bisphenol-F-type epoxy resin, phenol novalec-type
epoxy resin, cresol novalec-type epoxy resin, polyepoxy compounds
based on aromatic amines and epichlorohydrin, polyglycidyl
derivatives of phenolic compounds; polyglycidyl derivatives of
phenol-formaldehyde novalecs, polyglycidyl adducts of amines,
aminoalcohols and polycarboxylic acids; and combinations
thereof.
31. An integrated circuit chip as in claim 28, wherein said curing
agent is selected from the group consisting of anhydride compounds,
amine compounds, amide compounds, imidazole compounds, and
combinations thereof.
32. An integrated circuit chip as in claim 28, wherein said
inorganic filler component may be selected from the group
consisting of materials constructed of or containing reinforcing
silicas, aluminum oxide, silicon nitride, aluminum nitride,
silica-coated aluminum nitride, boron nitride, and combinations
thereof.
33. An integrated circuit chip as in claim 25, wherein said fluxing
agent comprises an organic acid.
34. An integrated circuit chip as in claim 33, wherein said fluxing
agent comprises a material selected from the group consisting of
abietic acid, adipic acid, ascorbic acid, acrylic acid, citric
acid, 2-furoic acid, malic acid, and polyacrylic acid.
35. An integrated circuit chip as in claim 25, wherein said fluxing
agent comprises a latent organic acid.
36. An integrated circuit chip as in claim 25, wherein said fluxing
agent comprises a thermally-activatable blocked organic acid.
37. An integrated circuit chip as in claim 25, wherein said fluxing
agent further comprises an epoxy compound capable of drying to form
a film of said fluxing agent on said electrical contacts and
capable of reacting with at least one of said first or said second
thermosetting underfill compositions upon curing of said first and
second thermosetting underfill compositions.
38. An integrated circuit chip as in claim 25, wherein said chip
die is constructed of material selected from the group consisting
of silicon and germanium.
39. An integrated circuit chip as in claim 25, wherein said chip
die is coated with a material selected from the group consisting of
a polyimide-based material, poly-benzocyclobutane-based material,
and a silicone nitride-based material.
40. An integrated circuit chip as in claim 25, wherein said carrier
substrate is constructed of a material selected from the group
consisting of Al.sub.2O.sub.3, silicon nitride, mullite, polyimide,
glass-reinforced epoxy, acrylonitrile-butadiene-styrene, and
phenolic substrates.
41. An integrated circuit chip as in claim 25, wherein said
electrical contacts comprise solder bumps.
42. An integrated circuit chip as in claim 25, wherein reaction
products of at least one of said first or said second thermosetting
underfill compositions are controllably degradable when exposed to
appropriate conditions.
43. An integrated circuit chip as in claim 42, wherein at least one
of said first or said second thermosetting underfill compositions
comprises a curable compound having at least one thermally
cleavable linkage, a curing agent for promoting cure of said
curable compound, and optionally, an inorganic filler
component.
44. An integrated circuit chip as in claim 43, wherein said
compound having at least one thermally cleavable linkage is
selected from the group consisting of diepoxides including acyclic
acetal groups and full and partial episulfide equivalents thereof;
diepoxides including secondary carbonyl linkages and full and
partial episulfide equivalents thereof; diepoxides including
tertiary carbonyl linkages and full and partial episulfide
equivalents thereof; diepoxides including an aromatic moiety within
the structure and full and partial episulfide equivalents thereof;
and combinations thereof.
45. An integrated circuit chip as in claim 25, wherein said first
thermosetting underfill composition when cured provides a first
dielectric layer in contact with said chip die and having a
coefficient of thermal expansion compatible with said chip die, and
said second thermosetting underfill composition when cured provides
a second dielectric layer in contact with said first dielectric
layer and said carrier substrate and having a coefficient of
thermal expansion compatible with said carrier substrate and said
first dielectric layer.
46. A integrated circuit chip as in claim 25, wherein said chip die
comprises a packaged integrated circuit, and said electrical
contacts are arranged on said packaged integrated circuits for
providing electrical interconnection with said electronic circuitry
of said carrier substrate.
47. An circuit assembly comprising the assembled product of claim
25.
48. A method for assembling an integrated circuit assembly
comprising: a) providing an integrated circuit chip in accordance
with claim 25; b) mating said integrated circuit chip with a
carrier substrate to form a mated assembly; and c) exposing said
mated assembly to temperature conditions sufficient to promote
electrical interconnection between said integrated circuit chip and
said carrier substrate and to cure said first and said second
thermosetting underfill compositions, thereby adhering said
integrated circuit chip to said carrier substrate.
49. An integrated circuit chip assembly comprising: a) a carrier
substrate; and b) a chip die electrically interconnected with said
carrier substrate through the use of solder having had a fluxing
agent disposed on at least a portion thereof, said chip die adhered
to said carrier substrate through a cured thermoset underfill
compound which is substantially free of residue from said fluxing
agent, said fluxing agent having been distinct from a curable
thermosetting underfill composition from which said cured thermoset
underfill compound is formed.
50. An integrated circuit chip assembly as in claim 49, wherein
said thermoset underfill compound is controllably degradable when
exposed to appropriate conditions.
51. An integrated circuit chip assembly as in claim 49, further
comprising a second thermoset underfill compound distinct from said
thermoset underfill compound between said chip die and said carrier
substrate.
52. An integrated circuit chip assembly as in claim 51, wherein
said second thermoset underfill compound is controllably degradable
when exposed to appropriate conditions.
53. An integrated circuit chip assembly as in claim 49, wherein
said chip die comprises a packaged integrated circuit.
54. A method for assembling an integrated circuit chip comprising
the steps of: a) providing a chip die having flowable electrical
contacts arranged in a predetermined pattern thereon; b) applying a
fluxing agent over at least a portion of said electrical contacts;
and c) dispensing a curable thermosetting underfill composition in
a flowable form on said chip die around said electrical contacts,
said thermosetting underfill composition being distinct from said
fluxing agent.
55. A method as in claim 54, further comprising drying said fluxing
agent after said applying step b).
56. A method as in claim 55, further comprising reducing the
flowability of said thermosetting underfill composition after said
dispensing step c).
57. A method as in claim 55, further comprising a step d)
dispensing a second thermosetting underfill composition in a
flowable form on said thermosetting underfill composition around
said electrical contacts, said second thermosetting underfill
composition being distinct from said fluxing agent and said first
thermosetting underfill composition.
58. A method as in claim 57, further comprising reducing the
flowability of said thermosetting underfill composition and said
second thermosetting composition after said dispensing step d).
59. A method as in claim 57, wherein any of said applying and said
dispensing steps b), c) and d) comprise screen printing, stencil
printing, jet printing, pad printing, or offset printing.
60. An integrated circuit assembly comprising: a) a carrier
substrate; and b) a chip die electrically interconnected with said
carrier substrate through the use of solder having had disposed on
at least a portion thereof a fluxing agent, said chip die adhered
to said carrier substrate through a cured thermoset composite which
is substantially free of residue from said fluxing agent, said
cured thermoset composite comprising: i) a first dielectric layer
having a coefficient of thermal expansion compatible with said chip
die; and ii) a second dielectric layer having a coefficient of
thermal expansion compatible with said circuit board substrate;
wherein said fluxing agent was directly on a surface of said solder
and distinct from curable thermosetting compositions from which
said dielectric layers are formed.
61. A circuit assembly as in claim 60, wherein said chip die
comprises a packaged integrated circuit.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority to U.S. Ser. No.
60/248,419 filed Nov. 14, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to assemblies for connecting
circuitry. More particularly, the invention relates to mounting
assemblies and methods for providing electrical connection between
electronic circuitry.
[0004] 2. Brief Description of Related Technology
[0005] In recent years, the popularity of small-sized electronic
appliances, such as camera-integrated video tape recorders and
portable telephone sets, has made size reduction of large-scale
integration desirable. As a result, chip size or chip scale
packages are being used to reduce the size of packages
substantially to that of bare chips. Such chip scale packages
include a semiconductor chip mounted on a carrier substrate, which
improves the characteristics of the electronic device while
retaining many of the operating features, thus serving to protect
semiconductor bare chips and facilitate testing thereof.
[0006] Upside down integrated circuits, commonly referred to as
"flip-chips", are now gaining popularity as well. Flip-chips are
manufactured using solder bump technology, in which solder bumps
are deposited on solder-wettable metal terminations on a die or
chip and a matching pattern of solder-wettable terminations on the
substrate. With flip-chips, the solder bumps are placed on the
integrated circuit terminals while the chip is in wafer form, and
then, after singulation, a chip is flipped and aligned to the
circuit board substrate. A fluxing agent is applied and the solder
bumps are re-flowed by heating to establish bonding between the
chip and the substrate, with all the joints being made
simultaneously by melting the solder.
[0007] When the resulting circuit board assembly is exposed to
thermal cycling, the reliability of the solder connection between
the circuit board and the chip often becomes suspect. Commonly,
after a chip is mounted on a circuit board, the space between the
chip and the circuit board is filled with a sealing resin (often
referred to as underfill sealing) in order to reinforce against
stresses caused by thermal cycling. Such underfill encapsulation
has gained considerable acceptance in the electronics industry,
with epoxy-based resin materials being most commonly used in such
applications. Moreover, the expansion coefficients of the underfill
sealing can be adjusted, for example, by the addition of low
thermal-expansion fillers, such as glass or ceramics, thus reducing
the level of thermal stress that develops between the substrate and
the underfill sealing. The underfill sealing thus provides
structural reinforcement, which delocalizes the thermal expansion
stress, thereby improving heat shock properties and enhancing the
reliability of the structure.
[0008] Also, the underfill material helps adhere the chip to the
substrate. As such, the underfill material should exhibit high
cohesive strength to the die and the circuit board surface, and
retain significant strength within the environment encountered by
the electronic device, for example, during heat-up and cool-down
cycles associated with on/off powering of the electronics, as well
as climatic changes in temperature and humidity.
[0009] Application of underfill sealing typically involves
dispensing the underfill material onto one or more edges of the
flip-chip assembly after it has been assembled and the solder bumps
affixed to the substrate. Capillary action draws the underfill
material through the gap between the chip and the substrate. Such
underfill techniques are time consuming, and complete filling of
the underfill sealing between the chip and the substrate can be
difficult to achieve, thus reducing the protection level afforded
through the underfill sealing.
[0010] In an attempt to overcome these issues and to eliminate
processing steps, underfill sealants incorporating fluxing agents
for bonding of the solder bumps have been proposed. For example,
U.S. Pat. Nos. 5,985,043 and 5,985,486 disclose polymerizable
fluxing agents, which act as an adhesive to bond the chip to the
substrate. Such polymerizable fluxing agents are based on
polycarboxylic acids having olefinic linkages, compositions of that
are curable upon exposure to heat. The thinking here is that the
underfill sealant incorporating such polymerizable fluxing agents
can be applied to the chip during the wafer stage of chip
manufacture, often referred to as wafer-applied fluxing underfill,
in which a plurality of chips are manufactured in one piece and
later cut into individual chips. By pre-applying onto the wafer the
fluxing agent/underfill sealant combination, the chip should only
need to be placed on the substrate, with solder re-flow and
underfill curing occurring to affix the chip thereto. In practice,
however, including the fluxing agent and underfill sealant in a
single composition tends to compromise adhesion and mechanical
strength of the underfill sealant.
[0011] Further, in some applications, the desirability of component
removal may be of a concern, for example, when chip failure occurs.
To avoid destroying or scrapping the entire assembly, it has been
proposed to include reworkable adhesive materials in the assembly
process. Such reworkable adhesive materials may be used as the
underfill encapsulant adhesive, thereby providing reworkability to
enable removal and replacement of one or more defective die. Such
reworkable underfill materials typically involve thermally
cleavable epoxy-based polymers, which will decompose rapidly when
exposed to a high enough temperature. For example, U.S. Pat. Nos.
5,948,922 (Ober) and 5,973,033 (Ober), each refer to a certain
class of compounds and compositions based on such compounds which,
when cured, provide decomposable compositions capable of being
reworked.
[0012] U.S. Pat. Nos. 5,512,613 (Afzali-Ardakani), 5,560,934
(Afzali-Ardakani) and 5,932,682 (Buchwalter), each refer to a
reworkable thermoset composition based on a diepoxide component in
which the organic linking moiety connecting the two epoxy groups of
the diepoxide includes an acid cleavable acyclic acetal group. With
such acid cleavable acyclic acetal groups forming the basis of the
reworkable composition, a cured thermoset need only be introduced
to an acidic environment in order to achieve softening and a loss
of much of its adhesiveness.
[0013] U.S. Pat. No. 5,872,158 (Kuczynski) refers to thermosetting
compositions capable of curing upon exposure to actinic radiation,
which are based on acetal diacrylates, and reaction products of
which are reported to be soluble in dilute acid.
[0014] U.S. Pat. No. 5,760,337 (Iyer) refers to thermally
reworkable crosslinked resins to fill the gap created between a
semiconductor device and a substrate to which it is attached. These
resins are produced by reacting a dienophile (with a functionality
greater than 1) with a 2,5-dialkyl substituted furan-containing
polymer.
[0015] International Patent Publication No. PCT/US98/00858 refers
to a thermosetting resin composition capable of sealing
underfilling between a semiconductor device including a
semiconductor chip mounted on a carrier substrate and a circuit
board to which said semiconductor device is electrically connected.
The composition includes about 100 parts by weight of an epoxy
resin, about 3 to about 60 parts by weight of a curing agent, and
about 1 to about 90 parts by weight of a plasticizer. Here, the
area around the cured thermoset is to be heated at a temperature of
about 190.degree. C. to about 260.degree. C. for a period of time
ranging from about 10 seconds to about 1 minute in order to achieve
softening and a loss of much of its adhesiveness.
[0016] The additional chemistry built into such reworkable polymers
to provide the ability to controllably degrade under appropriate
conditions, however, oftentimes detracts from the overall
effectiveness of the underfill sealing in terms of strength,
adhesion, and moisture resistance.
[0017] U.S. Pat. No. 6,121,689 discloses a semiconductor flip-chip
package, which includes a polymerizable fluxing agent. FIGS. 1 and
2 herein depict flip-chip structures as set forth in the '689
patent. As is apparent, the flip-chip structure of FIG. 1 includes
a chip 10 having solder bumps 14 pre-assembled thereon for
electrical connection with solder pads 12 of a substrate 20 through
the use of an encapsulant 22. In further embodiments, a fluxing
adhesive may be used to adhere the chip 10 to the substrate 20.
Moreover, as shown in FIG. 2, the structure may also include a
multi-layer encapsulant material 36, including attachment and
stress distribution layers 38 and 40, and thermoplastic
reworkability layer 42. This thermoplastic reworkability layer is
generally a meltable polymer such as a polyimide-siloxane
copolymer. As shown in FIG. 2, flux adhesive 34 may be provided
between the chip 10 and the substrate 20 for attachment of the chip
10 to the substrate 20. Adhesion and mechanical strength of the
underfill sealant may be compromised due to the incorporation of
the fluxing agent and the adhesive in a single composition. Also,
when an integrated circuit chip includes an encapsulant having a
fluxing adhesive incorporated therein, the fluxing adhesive may
adversely affect the encapsulant material, thereby reducing the
shelf stability or pot-life. Also, the use of a thermoplastic
material as the reworkability layer provides the assembly with
limited rework properties.
[0018] Notwithstanding the state of the art, it would be desirable
for an integrated circuit chip having an underfill sealant material
which provides excellent adherence and thermal shock properties
while allowing the substrate with which it is to be used to be
readily processed without compromising the physical properties of
the materials or the assembly.
SUMMARY OF THE INVENTION
[0019] The present invention is directed to an upside-down
flip-chip type integrated circuit chip, which is electrically
interconnectable with a carrier substrate, such as a circuit board
substrate. The integrated circuit chip includes a chip die having
electrical contacts which are flowable upon heating, such as solder
bumps, arranged in a predetermined pattern and capable of providing
electrical engagement and interconnection with electronic circuitry
on a surface of the carrier substrate. A fluxing agent is disposed
on a surface of the electrical contacts at a location capable of
providing effective fluxing activity to the electrical contacts of
the chip die and the electronic circuitry of the carrier substrate
when the chip die is mated with the carrier substrate. Also, a
curable thermosetting underfill composition is dispensed in a
flowable form over the chip die about the electrical contacts and
distinct from the fluxing agent. Upon mating of the chip die with
the carrier substrate to form a mated assembly and upon heating the
mated assembly to a temperature sufficient to render the electrical
contacts flowable, the electrical contacts flow to provide
electrical interconnection between the chip die and the carrier
substrate, and the thermosetting underfill composition cures,
thereby adhering the chip die to the carrier substrate. As such, a
circuit assembly is provided, with the thermosetting underfill
composition when cured providing a dielectric layer between the
chip die and the carrier substrate.
[0020] Desirably, the fluxing agent is disposed over substantially
the entire surface of the electrical contacts; with at least a
portion of the electrical contacts being exposed from the
thermosetting underfill composition. The fluxing agent is desirably
an organic acid, and may include an epoxy compound capable of
drying to form a film of the fluxing agent on the electrical
contacts.
[0021] The thermosetting underfill composition may include a
curable component, a curing agent for promoting cure of the curable
component and, optionally, an inorganic filler component.
Desirably, the curable component is an epoxy resin. In one
embodiment, the thermosetting underfill composition, when cured,
may be controllably degradable when exposed to appropriate
conditions. For example, the thermosetting underfill composition
may include a curable compound having at least one thermally
cleavable linkage.
[0022] The chip die may be provided as a chip scale package or a
packaged integrated circuit. As such, the electrical contacts are
arranged on the packaged integrated circuit for providing
electrical interconnection with the electronic circuitry of the
carrier substrate.
[0023] The present invention is also directed to a method for
assembling an integrated circuit assembly by mating such an
integrated circuit chip with a carrier substrate to form a mated
assembly. Such a mated assembly is then exposed to temperature
conditions sufficient to promote electrical interconnection between
the integrated circuit chip and the carrier substrate and to cure
the thermosetting underfill composition, thereby adhering the
integrated circuit chip to the carrier substrate.
[0024] As such, the present invention also provides an integrated
circuit chip assembly which includes a carrier substrate and a chip
die electrically interconnected with the carrier substrate through
the use of solder having had a fluxing agent disposed on at least a
portion thereof. The chip die is adhered to the carrier substrate
through a cured thermoset underfill compound which is substantially
free of residue from the fluxing agent, since the fluxing agent had
been distinct from a curable thermosetting underfill composition
from which the cured thermoset underfill compound is formed.
[0025] In yet a further embodiment, the present invention is
directed to an integrated circuit chip which is electrically
interconnectable with a carrier substrate, including a chip die
having electrical contacts which are flowable upon heating arranged
in a predetermined pattern and capable of providing electrical
engagement and interconnection with electronic circuitry on a
surface of the carrier substrate, and a fluxing agent disposed on a
surface of the electrical contacts at a location capable of
providing effective fluxing activity to the electrical contacts of
the chip die and the electronic circuitry of the carrier substrate
when the chip die is mated with the carrier substrate. The
integrated circuit chip further includes a first curable
thermosetting underfill composition dispensed in a flowable form
over the chip die about the electrical contacts and distinct from
the fluxing agent, and a second thermosetting underfill composition
dispensed in a flowable form over the first thermosetting underfill
composition about the electrical contacts and distinct from the
first thermosetting underfill composition and the fluxing agent.
Upon mating of the chip die with the carrier substrate to form a
mated assembly and upon heating the mated assembly to a temperature
sufficient to render the electrical contacts flowable, the
electrical contacts flow to provide electrical interconnection
between the chip die and the carrier substrate, and the first and
second thermosetting underfill compositions are cured, thereby
adhering the chip die to the carrier substrate. As such, an
integrated circuit chip is provided, with the first thermosetting
underfill composition when cured providing a first dielectric layer
in contact with the chip die and having a coefficient of thermal
expansion compatible with the chip die, and the second
thermosetting underfill composition when cured providing a second
dielectric layer in contact with the first dielectric layer and the
carrier substrate and having a coefficient of thermal expansion
compatible with the carrier substrate and the first dielectric
layer.
[0026] The first and second thermosetting compositions may each
individually include a curable component such as an epoxy resin, a
curing agent for promoting cure of the curable component and,
optionally, an inorganic filler component. Desirably, at least one
of the first or the second thermosetting underfill compositions,
when cured, is controllably degradable when exposed to appropriate
conditions, such as by including at least one thermally cleavable
linkage.
[0027] A method for assembling such an integrated circuit assembly
is also provided through the present invention by mating such an
integrated circuit chip with a carrier substrate to form a mated
assembly, and exposing the mated assembly to temperature conditions
sufficient to promote electrical interconnection between the
integrated circuit chip and the carrier substrate and to cure both
the first and second thermosetting underfill compositions, thereby
adhering the integrated circuit chip to the carrier substrate.
[0028] An integrated circuit assembly thus prepared is also
provided, which includes a carrier substrate and a chip die
electrically interconnected with the carrier substrate through the
use of solder having had disposed on at least a portion thereof a
fluxing agent, with the chip die adhered to the carrier substrate
through a cured thermoset composite which is substantially free of
residue from the fluxing agent. The cured thermoset composite
includes a first dielectric layer having a coefficient of thermal
expansion compatible with the chip die, and a second dielectric
layer having a coefficient of thermal expansion compatible with the
circuit board substrate. Prior to assembly, the fluxing agent was
directly provided on a surface of the solder and distinct from the
curable thermosetting compositions from which the dielectric layers
are formed.
[0029] The present invention is also directed to a method for
assembling an integrated circuit chip. Such a method involves
providing a chip die, which includes flowable electrical contacts,
arranged in a predetermined pattern on a surface. A fluxing agent
is applied over at least a portion of the electrical contacts and
desirably dried. A curable thermosetting underfill composition is
then dispensed in a flowable form on the chip die around the
electrical contacts, with the thermosetting underfill composition
being distinct from the fluxing agent. The flowability of this
thermosetting underfill composition may thereafter be reduced, such
as by drying. Optionally, a second thermosetting underfill
composition may be dispensed in a flowable form on the
thermosetting underfill composition around the electrical contacts,
with the second thermosetting underfill composition being distinct
from the fluxing agent and the first thermosetting underfill
composition. Similarly, the flowability of this second
thermosetting underfill composition may thereafter be reduced, as
with the first thermosetting underfill composition. The fluxing
agent and the first and second underfill compositions may be
applied and dispensed, for example, by screen printing, stencil
printing, jet printing, pad printing, or offset printing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIGS. 1 and 2 are schematic representations of underfilled
flip-chip structures as shown in U.S. Pat. No. 6,121,689;
[0031] FIG. 3 is a schematic representation of a circuit assembly
according to the present invention showing a flip-chip circuit chip
and a substrate prior to assembly;
[0032] FIG. 4 is a schematic representation of the circuit assembly
of FIG. 2 after assembly;
[0033] FIG. 5 is a schematic representation of a circuit assembly
according to an alternate embodiment of the present invention
showing a flip-chip circuit chip and a substrate prior to
assembly;
[0034] FIG. 6 is a schematic representation of the circuit assembly
of FIG. 5 after assembly;
[0035] FIG. 7 is a schematic representation of a circuit assembly
in a further embodiment of the present invention;
[0036] FIG. 8 is a schematic representation of a circuit assembly
in a further embodiment of the present invention;
[0037] FIG. 9 is a schematic representation of a circuit assembly
including a chip scale package assembled to a substrate in a
further embodiment of the present invention; and
[0038] FIG. 10 is a schematic representation of a circuit assembly
including a chip scale package assembled to a substrate according
to a further embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] Referring to the drawings in which like reference characters
refer to like parts throughout the several views thereof, a circuit
assembly 50 is depicted in FIGS. 3 and 4, including an upside down
flip-chip type semiconductor chip in the form of integrated circuit
chip 60, and a carrier substrate such as circuit board substrate
70. Integrated circuit chip 60 includes a chip die 62. Chip die 62
may be constructed of any material known in the art. For example,
chip die 62 may be constructed of silicon, germanium, or the like.
Chip die 62 may also be coated with a material, which is capable of
passivating environmental corrosion, such as a polyimide-,
poly-benzocyclobutane-, or silicone nitride-based material.
[0040] Substrate 70 may also be constructed of any material known
in the art. For example, substrate 70 may be constructed from
ceramic substrates including Al.sub.2O.sub.3, silicon nitride
(SiN.sub.3), and mullite (Al.sub.2O.sub.3--SiO.sub.2); substrates
or tapes of heat-resistant resins, such as polyimides; substrates
of glass-reinforced epoxy; substrates of
acrylonitrile-butadiene-styrene (ABS); and phenolic substrates, and
the like.
[0041] Chip die 62 includes circuitry on a chip surface 64 thereof,
including a plurality of electrical contact pads, such as
metallized contact pads (not shown) which are arranged in a
predetermined pattern, as is known in the art. These electrical
contact pads are arranged to receive a plurality of corresponding
electrical contacts in the form of solder bumps 82 connected to the
contact pads of the chip die 62. Further, substrate 70 includes
electronic circuitry on a substrate surface 74 thereof, including a
plurality of electrical contact pads, such as solder pads 88. Each
of solder pads 88 and solder bumps 82 are metallized so as to
become solderable and electrically conductive, thus providing
electrical interconnection between the circuitry on chip die 62 and
the circuitry on substrate 70 when integrated circuit chip 60 is
mounted on substrate 70, as will be described in more detail
herein. While the present FIGS. depict two solder bumps 82 on chip
die 62 and two corresponding solder pads 88 on substrate 70 for
purposes of demonstrating the present invention, it should be
understood that the number of solder bumps 82 and solder pads 88
may be varied according to the particular desired use and the
particular configuration of the circuit chip, and the specific
configuration depicted herein should not be considered as limiting
of the present invention.
[0042] Solder bumps 82 may be applied to chip die 62 in any manner
as is known in the art. Solder bumps 82 may incorporate any known
solder alloy, provided that such solder is flowable upon heating.
Selection of the solder alloy for solder bumps 82 depends, in part,
on the particular melting point and on the material used for the
chip and substrate. For example, solders having a high melting
point, such as high lead or lead-free solders, are useful with
alumina ceramic substrates. Lower melting solder alloys, such as
eutectic tin/lead solder or lead/indium solder, are particularly
useful when polymeric circuit boards are used, due to their lower
melting point. Of course, the specific solder useful for solder
bumps 82 will also depend upon the specific compositions used in
the underfill components of the present invention, as will be
discussed in more detail.
[0043] Each of solder bumps 82 includes a fluxing agent 85 disposed
as a layer or film extending over the surface of each solder bump
82. Fluxing agent 85 provides fluxing action for the soldering
operation. Fluxing agents which are particularly useful in the
present invention include carboxylic acids of the general formula:
1
[0044] where R is hydrogen, alkyl, aryl, or a polymer, and n is an
integer from 1-50. Non-limiting examples of fluxing agents useful
in the present invention include materials selected from abietic
acid, adipic acid, ascorbic acid, acrylic acid, citric acid,
2-furanoic acid, malic acid, salicylic acid, glutaric acid, pimelic
acid, polyacrylic acids, and other acid functionalities, such as
phenol and derivatives thereof, and sulfonic acids, such as toluene
sulfonic acids.
[0045] A particularly desirable one is DIACID 1550 which is a
liquid monocyclic twenty-one carbon dicarboxylic acid derived from
tall oil fatty acids; specifically it is 1-n-heptyl carboxylic
acid, 2-carboxylic acid, 4-n-hexyl-cyclohexenes, available from
Westvaco Oleo Chemicals.
[0046] Other organic acids useful as fluxing agents are those
having the general formula: 2
[0047] where R is an electron-withdrawing group, such as fluorine,
chlorine, bromine, iodine, sulfur, nitrile, hydroxyl, or
benzyl.
[0048] It is also contemplated through the present invention that
fluxing agent 85 may be a latent organic acid, such as a
thermally-activatable blocked organic acid, which is capable of
providing fluxing activity when the temperature is increased above
a temperature which causes release of a constituent blocking the
acid group of the composition.
[0049] Fluxing agent 85 may be provided, for example, in the form
of a liquid composition, which is coated onto solder bumps 82. Such
a liquid composition preferably includes a fluxing agent dissolved
or dispersed in a suitable solvent. During application of fluxing
agent 85 to solder bumps 82, the solvent is driven off of the
composition, resulting in fluxing agent 85 present as a coated film
layer. Such coated film layer desirably has a film thickness from
about 0.25 to about 2 mil, more desirably from about 0.5 to about 1
mil.
[0050] Fluxing agent 85 may further include an epoxy compound. Such
an epoxy compound acts as a carrier for the fluxing agent, in that
the fluxing agent can be disposed on the surface of solder bumps 82
and dried, with the epoxy compound providing a vehicle for the
fluxing agent to remain as a film on the surface of solder bumps
82. Moreover, such an epoxy compound may be capable of reacting
with the thermosetting underfill compositions provided in circuit
assembly 50.
[0051] Fluxing agent 85 is disposed on a surface of solder bumps 82
at a location capable of providing effective fluxing activity for
soldering solder bumps 82 with solder pads 88 when chip die 62 is
mated with substrate 70. As such, fluxing agent 85 may be disposed
as a film, covering the entire surface of solder bumps 82.
Alternatively, fluxing agent 85 may be disposed over only a small
portion of solder bumps 82, representing the portion of solder
bumps 82 to be mated and soldered with solder pads 88.
[0052] Fluxing agent 85 may be coated on solder bumps 82 in any
manner capable of providing a substantially consistent coating over
solder bumps 82, thereby insuring adequate fluxing action during
soldering. For example, fluxing agent 85 may be stencil printed or
screen printed onto solder bumps 82. Alternatively, fluxing agent
85 may be printed onto solder bumps 82 through an offset gravure
printing method, such as pad printing. In such a method, a gravure
or cliche is patterned with the area to be printed, and ink is
transferred from the cliche to the part to be printed using a
silicon pad. Extrusion coating processes and jet printing processes
may also be used to coat fluxing agent 85 onto solder bumps 82.
[0053] In flip-chip mounting arrangements, mounting of the chip die
to the substrate surface typically results in a gap, such as gap
55, formed between the chip die 62 and the substrate 70, around
solder bumps 82 between the chip surface 64 of the integrated
circuit chip 60 and the substrate surface 74 of substrate 70. Gap
55 is encapsulated with an underfill component 90, providing an
underfill material between chip die 62 and substrate 70, and for
adhering integrated circuit chip 60 to substrate 70. Desirably,
chip die 62, having separate discrete solder bumps 82 pre-assembled
thereon, is pre-coated with fluxing agent 85 over solder bumps 82
and with underfill component 90 prior to assembly of chip die 62
with substrate 70 to alleviate the underfill problems of the prior
art processes, and to overcome the performance limitations of
substrates which are pre-coated with a homogeneous combination of
adhesive material, fluxing agent, and curing agent. Thus, the
present invention provides, in one embodiment, an integrated
circuit chip having electrical contacts pre-coated with a fluxing
agent thereon, and including a pre-coated underfill component.
[0054] More particularly, in prior art processes for flip-chip
mounting arrangements, such as U.S. Pat. No. 6,121,689 discussed
above, the chip die commonly includes a fluxing adhesive material
coated on the surface to act as an underfill material, with holes
drilled through the fluxing adhesive material and filled with an
electrically conductive material, such as solder, for providing
electrical interconnection with a substrate when the chip die is
mated with the substrate and the solder is reflowed. In such an
arrangement, the fluxing agent is disposed throughout the adhesive
underfill material, allowing for fluxing during heating of the
assembly for solder reflow. Fluxing agents, however, are not
traditionally compatible with materials particularly useful as
underfill materials, such as epoxy thermosetting resins and/or
curing agents used with such resins. As such, including the fluxing
agent within the underfill material can adversely affect the
storage stability or pot-life of the adhesive underfill material.
Moreover, during heating of the assembly for fluxing activity and
solder reflow, residue from the fluxing agent may be dispersed
throughout the entire adhesive underfill material, since the
fluxing agent is a component within the adhesive underfill
material. Such residue may adversely affect the curing properties
of the adhesive underfill material, which may result in
insufficient curing, and improper adhesion between the chip die and
the substrate.
[0055] In the present invention, the fluxing agent 85 is directly
disposed only on a surface of the solder bumps 82, and the
underfill component is a separate and discrete component which is
distinct from the fluxing agent. Accordingly, the fluxing agent
will not adversely affect the storage stability or pot-life of the
underfill component, and any residue from the fluxing agent will
not adversely affect the cure of the underfill component.
[0056] Underfill component 90 is in contact with chip die 62 on
chip surface 64. Underfill component 90 provides circuit assembly
50, after assembly as an integrated unit, with high adhesive
strength for adhering chip die 62 to substrate 70, and with low
thermal expansion for increased reliability of circuit assembly 50.
Underfill component 90, when cured, also provides a dielectric
layer between chip die 62 and substrate 70.
[0057] As noted above, the underfill component of the present
invention is a curable composition, which provides high adhesive
strength and low thermal expansion. Thermosetting resin
compositions are particularly useful as the curable underfill
component. Such a thermosetting resin composition may broadly
include (a) a curable resin component; (b) an optional inorganic
filler component; and (c) a curing agent component including an
anhydride component, a nitrogen-containing component, such as an
amine compound, an amide compound, and/or an imidazole compound,
and/or combinations thereof.
[0058] Typically, the composition includes about 10 to about 60
weight percent of the curable resin component by weight of the
total composition; about 0 to about 60 weight percent of the
inorganic filler component; and 0.01 to about 60 weight percent of
the curing agent component, of which about 0 to about 60 weight
percent thereof is comprised of an anhydride compound, 0 to about 5
weight percent thereof is comprised of an amide compound, such as a
cyano-functionalized amide, like dicyandiamide, and 0 to about 2
weight percent thereof is comprised of an imidazole compound.
[0059] Of course, depending on the particular set of properties
desirable for a composition destined for a specific purpose, these
values may vary somewhat. Such variation may be achieved without
undue experimentation by those persons skilled in the art, and
accordingly are contemplated within the scope of the present
invention.
[0060] The curable resin component may be selected from any known
resin. Desirably, the curable resin component may be any common
epoxy resin, such as a multifunctional epoxy resin.
[0061] Examples include the following multifunctional epoxy resins:
bisphenol-A-type epoxy resin (such as RE-310-S from Nippon Kayaku,
Japan, or EPON 1002f from Shell Chemical Co.), bisphenol-F-type
epoxy resin (such as RE-404-S from Nippon Kayaku, Japan), phenol
novalec-type epoxy resin, and cresol novalec-type epoxy resin (such
as "ARALDITE" ECN 1871 from Ciba Specialty Chemicals, Hawthorne,
N.Y.).
[0062] Other suitable epoxy resins include polyepoxy compounds
based on aromatic amines and epichlorohydrin, such as
N,N,N',N'-tetraglycidyl-4,4'- -diaminodiphenyl methane;
N-diglycidyl-4-aminophenyl glycidyl ether; and
N,N,N',N'-tetraglycidyl-1,3-propylene bis-4-aminobenzoate, as well
as polyglycidyl derivatives of phenolic compounds, such as those
available commercially under the tradename "EPON", such as "EPON"
828, "EPON" 1001, "EPON" 1009, and "EPON" 1031 from Shell Chemical
Co.; "DER" 331, "DER" 332, "DER" 334, and "DER" 542 from Dow
Chemical Co.; and BREN-S from Nippon Kayaku. Other suitable epoxy
resins include polyepoxides prepared from polyols and the like and
polyglycidyl derivatives of phenol-formaldehyde novalecs, the
latter of which are available commercially under the tradename
"DEN", such as "DEN" 431, "DEN" 438, and "DEN" 439 from Dow
Chemical. Cresol analogs are also available commercially under the
tradename "ARALDITE", such as "ARALDITE" ECN 1235, "ARALDITE" ECN
1273, and "ARALDITE" ECN 1299 from Ciba Specialty Chemicals
Corporation. SU-8 is a bisphenol-A-type epoxy novalec available
from Interez, Inc. Polyglycidyl adducts of amines, aminoalcohols
and polycarboxylic acids are also useful in this invention,
commercially available resins of which include "GLYAMINE" 135,
"GLYAMINE" 125, and "GLYAMINE" 115 from F.I.C. Corporation;
"ARALDITE" MY-720, "ARALDITE" 0500, and "ARALDITE" 0510 from Ciba
Specialty Chemicals and PGA-X and PGA-C from the Sherwin-Williams
Co.
[0063] And, of course, combinations of the different curable resins
are also desirable for use herein.
[0064] As an inorganic filler component, many materials are
potentially useful. For instance, the inorganic filler component
may often include reinforcing silicas, such as fused silicas, and
may be untreated or treated so as to alter the chemical nature of
their surface. Virtually any reinforcing fused silica may be
used.
[0065] Particularly desirable ones have a low ion concentration and
are relatively small in particle size (e.g., in the range of about
2-10 microns, such as on the order of about 2 microns), such as the
silica commercially available from Admatechs, Japan under the trade
designation SO-E5.
[0066] Other desirable materials for use as the inorganic filler
component include those constructed of or containing aluminum
oxide, silicon nitride, aluminum nitride, silica-coated aluminum
nitride, boron nitride, and combinations thereof.
[0067] The curing agent component should include materials capable
of catalyzing the polymerization of the epoxy resin component.
Desirable curing agents include an anhydride component, a
nitrogen-containing component, such as an amine compound, an amide
compound, and an imidazole compound, and combinations thereof.
[0068] Appropriate anhydride compounds for use herein include mono-
and polyanhydrides, such as hexahydrophthalic anhydride ("HHPA")
and methyl hexahydrophthalic anhydride ("MHHPA") (commercially
available from Lindau Chemicals, Inc., Columbia, S.C., used
individually or as a combination, which combination is available
under the trade designation "LINDRIDE" 62C) and
5-(2,5-dioxotetrahydrol)-3-methyl-3-cyclohexene-1,2-dicarboxylic
anhydride (commercially available from ChrisKev Co., Leewood, Kans.
under the trade designation B-4400).
[0069] Of course, combinations of these anhydride compounds are
also desirable for use in the compositions of the present
invention.
[0070] Examples of the amine compounds include aliphatic
polyamines, such as the di- or tri-aza compounds: 3
[0071] 1,5-diazabicyclo[3.4.0]non-ene; 4
[0072] 1,8-diazabicyclo[5.4.0]undec-7-ene ("DBU"); 5
[0073] 1,5,7-triazabicyclo[4.4.0]dec-5-ene;
[0074] the bicyclo mono- and di-aza compounds: 6
[0075] quinuclidine; 7
[0076] 1,4-diazabicyclo[2.2.2]octane;
[0077] the alkyl polyamines:
[0078] diethylenetriamine, triethylenetriamine,
diethylaminopropylamine, isophoronediamine and menthenediamine;
and
[0079] the aromatic polyamines:
[0080] m-xylenediamine, diaminodiphenylamine, and quinoxaline.
[0081] The nitrogen-containing compound portion of the salt thereof
ordinarily includes di-aza compounds or tri-aza compounds.
[0082] Of course, combinations of these amine compounds are also
desirable for use in the compositions of the present invention.
[0083] Aromatic polyamines and alicyclic polyamines are also
desirable as curing agents, particularly 4,4'-methylenedianiline
("MDA") and 4,4'methylenebis(cyclohexylamine) ("MCA"). Of course,
combinations of these amine compounds are also desirable for use in
the present invention.
[0084] Examples of amide compounds include cyano-functionalized
amides, such as dicyandiamide.
[0085] The imidazole compounds may be chosen from imidazole,
isoimidazole, and substituted imidazoles--such as alkyl-substituted
imidazoles (e.g., 2-methyl imidazole, 2-ethyl-4-methylimidazole,
2,4-dimethylimidazole, butylimidazole,
2-heptadecenyl-4-methylimidazole, 2-undecenylimidazole,
1-vinyl-2-methylimidazole, 2-undecylimidazole,
2-heptadecylimidazole, 1-benzyl-2-methylimidazole,
1-propyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole,
1-cyanoethyl-2-ethyl-4-methylimidazole,
1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole,
1-guanaminoethyl-2-methylimidazole and addition products of an
imidazole and trimellitic acid and the like, generally where each
alkyl substituent contains up to about 17 carbon atoms and
desirably up to about 6 carbon atoms), and aryl-substituted
imidazoles [e.g., phenylimidazole, benzylimidazole,
2-methyl-4,5-diphenylimidazole, 2,3,5-triphenylimidazole- ,
2-styrylimidazole, 1-(dodecyl benzyl)-2-methylimidazole,
2-(2-hydroxyl-4-t-butylphenyl)-4,5-diphenylimidazole,
2-(2-methoxyphenyl)-4,5-diphenylimidazole,
2-(3-hydroxyphenyl)-4,5-diphen- ylimidazole,
2-(p-dimethylaminophenyl)-4,5-diphenylimidazole,
2-(2-hydroxyphenyl)-4,5-diphenylimidazole,
di(4,5-diphenyl-2-imidazole)-b-
enzene-1,4,2-naphthyl-4,5-diphenylimidazole,
1-benzyl-2-methylimidazole, 2-p-methoxystyrylimidazole, and the
like, generally where each aryl substituent contains up to about 10
carbon atoms and desirably up to about 8 carbon atoms].
[0086] Examples of commercial imidazole compounds are available
from Air Products, Allentown, Pa. under the trade designation
"CUREZOL" 1B2MZ and from Synthron, Inc., Morganton, N.C. under the
trade designation "ACTIRON" NXJ-60; and from Borregaard Synthesis,
Newburyport, Mass. under the trade designation "CURIMID CN".
[0087] Of course, combinations of these imidazole compounds are
also desirable for use in the present invention.
[0088] The curing agent component may be used in an amount of from
about 2% to about 40% of the epoxy resin.
[0089] In addition, the composition may also include a flowability
agent, such as a silane and/or titanate.
[0090] Appropriate silanes for use herein include octyl trimethoxy
silane (commercially available from OSI Specialties Co., Danbury,
Conn. under the trade designation A-137), and methacryloxy propyl
trimethoxy silane (commercially available from OSI under the trade
designation A-174).
[0091] Appropriate titanates for use herein include titanium IV
tetrakis [2,2-bis[(2-propenyloxy)methyl]-1-butanolato-0]
[bis(ditridecylphosphito-- 0), dihydrogen].sub.2 (commercially
available from Kenrich Petrochemical Inc., Bayonne, N.J. under the
trade designation KR-55).
[0092] When used, the flowability agent may be used in an amount of
0 to about 2% of the curable resin.
[0093] In addition, adhesion promoters, such as the silanes,
glycidyl trimethoxysilane (commercially available from OSI under
the trade designation A-187) or gamma-amino propyl triethoxysilane
(commercially available from OSI under the trade designation
A-1100), may be used.
[0094] Conventional additives may also be used in the bulk
underfill component of the present invention to achieve certain
desired physical properties of the composition, the cured reaction
product, or both.
[0095] For instance, it may be desirable in certain instances
(particularly where a large volume of inorganic filler component is
used) to include a reactive co-monomer component for the epoxy
resin component, such as a reactive diluent.
[0096] Appropriate reactive diluents for use herein may include
monofunctional or certain multifunctional epoxy resins. The
reactive diluent should have a viscosity which is lower than that
of the epoxy resin component. Ordinarily, the reactive diluent
should have a viscosity less than about 250 cps. In the event such
a monofunctional epoxy resin is included as a reactive diluent,
such resin should be employed in an amount of up to about 50 parts
based on the total of the epoxy resin component.
[0097] The monofunctional epoxy resin should have an epoxy group
with an alkyl group of about 6 to about 28 carbon atoms, examples
of which include C.sub.6-28 alkyl glycidyl ethers, C.sub.6-28 fatty
acid glycidyl esters and C.sub.6-28 alkylphenol glycidyl
ethers.
[0098] Commercially available monofunctional epoxy resin reactive
diluents include those from Pacific Epoxy Polymers, Richmond,
Mich., under the trade designations PEP-6770 (glycidyl ester of
neodecandoic acid), PEP-6740 (phenyl glycidyl ether) and PEP-6741
(butyl glycidyl ether).
[0099] Commercially available multifunctional epoxy resin reactive
diluents include those from Pacific Epoxy Polymers, under the trade
designations PEP-6752 (trimethylolpropane triglycidyl ether) and
PEP-6760 (diglycidyl aniline).
[0100] The thermosetting underfill composition useful in the
present invention may further contain other additives, such as
defoaming agents, leveling agents, dyes, and pigments. Moreover,
photopolymerization initiators may also be incorporated therein,
provided that such initiators do not adversely affect the
properties of the composition or reaction products formed
therefrom.
[0101] The thermosetting underfill component may further include a
compound, reaction products of which are controllably degradable
when exposed to appropriate conditions. For example, underfill
component 90 may include, at least in part, a reworkable
composition, which is controllably degradable, thus providing the
integrated circuit chip 60/substrate 70 interface with a point of
detachment, if, desired. As such, circuit assembly 50 includes a
structure such that integrated circuit chip 60 can be removed from
substrate 70, for example, in the event of failure of the chip.
Thus, circuit assembly 50 is provided with a point of detachment
which allows for repair, replacement, recovery, and/or recycling of
operative components from assemblies that have become, at least in
part, inoperative.
[0102] In such an embodiment, underfill component 90 may include
any composition which is curable to form a cured composition, thus
providing an adhesive for adhering or affixing chip die 62 to
substrate 70, and which is capable of being reworked under
appropriate conditions, such as by softening or degradation, with a
loss of adherence so as to release chip die 62 from substrate 70.
For example, underfill component 90 desirably includes a compound
having a cleavable linkage within the chemical structure thereof,
such as a thermally cleavable linkage. As such, underfill component
90 is capable of softening under exposure to elevated temperature
conditions, such as those in excess of the temperatures used to
cure the composition, and desirably in excess of those used to
reflow the solder. Such temperature exposure triggers the thermal
cleavability of the thermally cleavable linkage to provide such a
reworkable aspect to underfill component 90.
[0103] In such embodiments involving a reworkable composition, the
thermosetting underfill component desirably includes a curable
resin component, at least a portion of which includes at least one
thermally cleavable linkage, a curing agent for promoting cure of
the curable component, and optionally an inorganic filler
component. Desirably, the curable resin component includes an epoxy
or episulfide resin. As such, the thermosetting underfill component
may incorporate solely epoxy or episulfide resins which provide the
reworkable aspect of cured reaction products thereof, or it may
incorporate such epoxy or episulfide resins which, together with a
thermosetting epoxy composition, make up the thermosetting
underfill component. Desirably, the thermosetting underfill
component includes a reworkable epoxy or episulfide resin, a
thermosetting epoxy composition, and a curing agent in such
embodiments. For example, the reworkable epoxy or episulfide resin
may represent from 10% to 100% of the thermosetting underfill
component, more desirably from 40% to 60% of the thermosetting
underfill component.
[0104] The reworkable composition of thermosetting underfill
component includes any composition which is capable of thermally
curing, providing adhesive and sealing properties, and which is
capable of softening and degrading upon exposure to temperatures in
excess of the curing temperature, particularly in excess of the
solder reflow temperature. Desirably, the reworkable composition
included within the thermosetting underfill component includes a
compound having at least one thermally cleavable linkage selected
from diepoxides including acyclic acetal groups and full and
partial episulfide equivalents thereof; diepoxides including
secondary carboxyl or thiocarboxyl linkages and full and partial
episulfide equivalents thereof; diepoxides including tertiary
carboxyl linkages and full and partial episulfide equivalents
thereof; diepoxides including an aromatic moiety within the
structure and full and partial episulfide equivalents thereof;
compounds having at least two heteroatom-containing carbocyclic
structures pending from a core structure containing at least one
ether, thioether or carbonate linkage; and mixtures and
combinations thereof.
[0105] For example, epoxy compounds with at least one thermally
cleavable linkage useful as the reworkable composition may be
chosen from those within the following formula: 8
[0106] where each R.sub.1 is independently selected from hydrogen,
methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl,
C.sub.1-4 alkoxy, halogen, cyano and nitro; each R.sub.4 is
independently selected from hydrogen, methyl, ethyl, propyl and
isopropyl; R.sub.2 and R.sub.3 are each independently selected from
hydrogen, methyl, ethyl, propyl, phenyl, tolyl and benzyl, provided
that both R.sub.2 and R.sub.3 cannot be hydrogen, X is
independently selected from O and S, and m is 0 or 1.
[0107] The reworkable compositions may also be selected from epoxy
compounds including two oxycarbonyl groups, the first and second
oxycarbonyl groups being separated by an aromatic moiety. Such
compounds may be chosen from aromatic ester linkages and aliphatic
ester linkages with the aromatic moiety being present within the
network structure. Particularly desirable are tert-ester linkages
incorporating an aromatic moiety.
[0108] Desirable compounds having two oxycarbonyl groups separated
by an aromatic moiety include those having the following structure:
9
[0109] where R.sub.5 is phenylene; R.sub.6 and R.sub.7 are each
independently selected from methylene, ethylene, propylene, or
phenylene; R.sub.8 and R.sub.9 are each independently selected from
hydrogen, methyl, ethyl, and propyl, provided that both R.sub.8 and
R.sub.9 cannot be hydrogen; R.sub.10 and R.sub.11 are each
independently selected from hydrogen, methyl, ethyl, and propyl;
and X is independently selected from O and S. In particularly
desirable compounds, R.sub.5 is an ortho-substituted phenyl group,
a meta-substituted phenyl group, or a para-substituted phenyl
group. Additional desirable compounds include those having the
following formula: 10
[0110] where R.sub.12 is phenylene, R.sub.13 and R.sub.14 are
independently selected from secondary or tertiary aliphatic
moieties, and X is independently selected from O and S.
[0111] Compositions including a cleavable compound and including a
partial or complete episulfide within the compound are also useful
as reworkable compositions for the present invention. For example,
the curable composition may be: 11
[0112] where each R.sub.15 is independently selected from
C.sub.1-C.sub.10 alkyl, cycloalkyl, aryl, aralkyl, and alkaryl;
R.sub.16 and R.sub.17 are each independently selected from
hydrogen, methyl, ethyl, propyl, phenyl, hydroxyphenyl,
methoxyphenyl, tolyl, and benzyl; and X is independently selected
from O and S. For example, the curable compound may be: 12
[0113] where R.sub.16 and R.sub.17 are each independently selected
from hydrogen, methyl, ethyl, propyl, phenyl, hydroxyphenyl,
methoxyphenyl, tolyl, and benzyl; each R.sub.18 is independently
selected from hydrogen, methyl, ethyl, propyl, and isopropyl; each
R.sub.19 is independently selected from hydrogen, methyl, ethyl,
propyl, isopropyl, butyl, isobutyl, t-butyl, C.sub.1-C.sub.4
alkoxy, halogen, cyano and nitro; and X is independently selected
from O and S.
[0114] The curable compound may also be represented by the formula:
13
[0115] where each R.sub.15 is independently selected from
C.sub.1-C.sub.10 alkyl, cycloalkyl, aryl, aralkyl, and alkaryl;
R.sub.16 and R.sub.17 are each independently selected from
hydrogen, methyl, ethyl, propyl, phenyl, hydroxyphenyl,
methoxyphenyl, tolyl, and benzyl; m is 0 or 1; n is 0 or 1, and X
is independently selected from 0 and S.
[0116] Combinations of such compounds may also be used.
[0117] Other useful reworkable compositions include those having a
cyclic hydrocarbon moiety including an epoxy (or oxirane) or an
episulfide (or thiirane) group, as well as an aromatic ether moiety
also including an oxirane or thiirane group. The cyclic hydrocarbon
moiety and the aromatic ether moiety are joined to each other
through a carboxyl-containing linkage or a thiocarboxyl-containing
linkage.
[0118] Each moiety of the compound may independently include either
an epoxy group or an episulfide group. For example, the cyclic
hydrocarbon moiety of the present invention desirably includes an
oxirane group, such as a cycloaliphatic epoxy moiety.
Alternatively, the cyclic hydrocarbon moiety may include a thiirane
group, such as a cycloaliphatic episulfide moiety. Also, the
aromatic ether moiety desirably includes an oxirane group, such as
an aromatic glycidyl ether moiety. Alternatively, the aromatic
ether moiety may include a thiirane group, such as an aromatic
thioglycidyl ether moiety.
[0119] Such useful compounds may be defined by the following
formula: 14
[0120] where R.sub.20 is selected from hydrogen, methyl, ethyl,
propyl, isopropyl, butyl, isobutyl, tert-butyl, C.sub.1-4 alkoxy,
halogen, cyano, nitro and phenyl; each R.sub.21 is independently
selected from hydrogen, methyl, ethyl, propyl, and isopropyl;
R.sub.22 and R.sub.23 are independently selected from hydrogen,
methyl, ethyl, propyl, phenyl, tolyl, and benzyl; R.sub.24 is
independently selected from hydrogen, methyl, ethyl, propyl,
isopropyl, butyl, isobutyl, tert-butyl, C.sub.1-4 alkoxy, halogen,
cyano, nitro and phenyl; p is an integer from 0-4; and X and Y are
independently selected from O and S.
[0121] As indicated, Y can be O or S, thus providing the structure
with a carboxyl or thiocarboxyl linkage between the cyclic
hydrocarbon moiety and the aromatic ether moiety. Desirably, Y is
oxygen, producing a carboxyl linkage between the moieties.
[0122] Further, at least one of R.sub.22 and R.sub.23 may be other
than hydrogen, producing a secondary linkage between the
cycloaliphatic moiety and the aromatic ether moiety. More
desirably, neither R.sub.22 nor R.sub.23 are hydrogen, producing a
tertiary linkage between the cycloaliphatic moiety and the aromatic
moiety.
[0123] The reworkable composition may further be a curable resin
component chosen from those having at least two
heteroatom-containing carbocyclic structures pending from a core
structure, with the core structure containing at least one linkage
selected from ether, thioether, carbonate, and combinations
thereof, which linkage is capable of being reworked under
appropriate conditions so as to lose its adhesiveness. For example,
the curable resin may be represented by the following structure:
15
[0124] The box may represent one or more structural linkages
including aromatic rings(s) or ring system(s), with or without
interruption or substitution by one or more heteroatoms, examples
of which are given below.
[0125] X.sup.1, X.sup.2, X.sup.a, and X.sup.b may be the same or
different and represent the heteroatoms, oxygen and sulfur. The
letter designations, m and m', represent integers within the range
of 1 to 3, n and n' represent integers within the range of 0 to 8,
and o and o' represent integers within the range of 1 to 3. The box
of the core structure of aromatic rings within the curable resin of
structure VIII may be individual aromatic rings, or aromatic ring
systems having multiple aromatic units joined in fused ring
systems, joined in bi-aryl (such as biphenyl) or bis-aryl (such as
bisphenol A or bisphenol F, or bisphenol compounds joined by a
heteroatom) systems, joined in cycloaliphatic-aromatic hybrid ring
systems, or joined in oligomeric (such as novalec-type) systems,
examples of which include, among others, naphthalene, anthracene,
phenanthracene, and fluorene.
[0126] For instance, the box may represent the structural linkage:
16
[0127] where Z may or may not be present and when present is
carbon, or the heteroatom, oxygen or sulfur. Or the box may
represent a phenylene group. Either of these representations may
bear substitution at one or more locations on the aromatic ring(s)
with functional groups ordinarily present on aromatic rings(s),
such as alkyl, alkenyl, halo, nitro, carboxyl, amino, hydroxyl,
thio, and the like.
[0128] For instance, particularly desirable curable resins within
structure VIII include MPG,
bis[4(2,3-epoxy-propylthio)phenyl]-sulfide (CAS Reg. No.
84697-35-8), available commercially from Sumitomo Seika Chemicals
Co., Ltd., Osaka, Japan and XBO, xylene bisoxetane (CAS Reg. No.
142627-97-2), available commercially from UBE Industries, Ltd.,
Tokyo, Japan.
[0129] The reworkable composition may further be a curable resin
represented by the following structure: 17
[0130] where X.sup.1 and X.sup.2 are as above; X.sup.c and X.sup.d
may be the same or different, may or may not be present, and when
present represent alkyl, alkenyl, aryl, and the like; and the
letter designations, m and m' are as above.
[0131] The heteroatom-containing carbocyclic structures pending
from the core structure may be three-, four-, or five- membered
rings with the heteroatom being an oxygen and/or sulfur atom. These
ring structures cross-link with one another under appropriate
conditions to form reaction products of the compositions.
[0132] The carbonate linkage is degradable upon exposure to
elevated temperature conditions, with or without the presence of
acid. This linkage is capable of degrading to liberate carbon
dioxide gas.
[0133] The temperature used to effect such degradation of
compositions within the scope of the present invention may be as
great as 50.degree. C. lower than the temperatures required to
degrade ordinary epoxy-based compositions used for this purpose,
such as those based on bisphenol-A-type epoxy resins or
bisphenol-F-type epoxy resins, which are ordinarily in the vicinity
of about 300.degree. C. or more. Moreover, the temperature used to
effect such degradation should be above the reflow temperature of
the solder, so as to result in reflow of the solder during such
degradation. Such solder reflow temperatures are ordinarily in the
vicinity of about 200.degree. C. to 230.degree. C.
[0134] A particularly desirable curable resin within structure IX
includes CBO, carbonate bisoxetane (CAS Reg. No. 60763-95-3),
available commercially from UBE Industries, Ltd., Tokyo, Japan.
[0135] The curable resin may also be an epoxy resin where at least
a portion of such epoxy resin includes an epoxy resin having at
least one alkylene oxide residue position adjacent at least one
terminal epoxy group. The epoxy resin may be based on mono- or
multi-functional aliphatic epoxies, epoxies with a cycloaliphatic
ring structure or system, or epoxies with an aromatic ring
structure or system, and combinations thereof.
[0136] The epoxy compounds with at least one thermally cleavable
anhydride linkage may be chosen from those within the following
formula: 18
[0137] where R.sub.25 and R.sub.28 are each independently selected
from hydrogen, methyl, ethyl, propyl, isopropyl, but-yl, isobutyl,
t-butyl, C.sub.1-4 alkoxy, halogen, cyano and nitro, and R.sub.26
and R.sub.27 may or may not independently be present, but when
present are each independently selected from methylene, ethylene,
propylenes, and butylenes, and arylenes, such as phenylenes,
benzylenes, phenoxylenes, benzyoxylenes and derivatives thereof,
and when R.sub.26 and R.sub.27 are present, R.sub.25 and R.sub.26
taken together, and/or R.sub.27 and R.sub.28 taken together, may
form a cyclic or bicyclic structure, such as a carbocyclic (e.g.,
cyclopentyl, cyclohexyl, cycloheptyl or norbornyl) or a
heterocyclic, which cyclic structures may be the same or different
and may be substituted by straight chain or branched alkyl or
alkenyl groups of from 1 to about 6 carbon atoms, which themselves
may be substituted by halogen, hydroxyl, or an alkoxy group, such
as about C.sub.1-4 alkoxy.
[0138] The reworkable composition may also include (a) an epoxy
resin component, at least a portion of which is a compound having
at least one linkage selected from oxiranes, thiiranes, and
combinations thereof, substituted on at least three of the
substitutable positions on the oxirane and/or thiirane carbons,
respectively, with an alkyl, alkenyl or aryl substituent having a
carbon content of 1 to about 12 carbon atoms, with or without
substitution or interruption by one or more heteroatoms or
halogens, as appropriate; and (b) a curing agent component selected
from anhydride compounds, amine compounds, amide compounds,
imidazole compounds, and combinations thereof.
[0139] Particular examples of useful compounds can be found in
International Patent Application No. PCT/US00/07452, published Sep.
28, 2000 entitled "Reworkable Thermosetting Resin Compositions",
International Patent Application No. PCT/US00/11878 entitled
"Reworkable Thermosetting Resin Compositions", U.S. Provisional
Application No. 60/222,392 filed Aug. 2, 2000 entitled "Reworkable
Thermosetting Resin Compositions", U.S. Provisional Application No.
60/232,813 filed Sep. 15, 2000 entitled "Reworkable Compositions
Incorporating Episulfide Resins", U.S. Provisional Application No.
60/230,098 filed Sep. 5, 2000 entitled "Reworkable Thermosetting
Resin Compositions and Compounds Useful Therein", U.S. Provisional
Application No. 60/198,747 filed Apr. 21, 2000 entitled "Reworkable
Thermosetting Resin Composition" and U.S. Provisional Application
No. 60/193,547 filed Mar. 31, 2000 entitled "Reworkable
Thermosetting Resin Composition", the disclosures of each of which
are hereby expressly incorporated herein by reference.
[0140] Particularly desirable are those compositions having a
rework temperature which is above the solder reflow
temperature.
[0141] As discussed, FIG. 3 depicts a circuit assembly 50 in which
integrated circuit chip 60 is prepared for attachment to substrate
70 for forming circuit assembly 50. As noted, the present invention
is directed to an integrated circuit chip which is electrically
interconnectable to a carrier substrate, such as integrated circuit
chip 60 as shown. Such integrated circuit chip 60 includes solder
bumps 82 including fluxing agent 85 disposed thereon, and further
includes underfill component 90 as a curable thermosetting
composition, capable of curing under exposure to appropriate
conditions to form a fully cured thermoset underfill material in a
solid form. Moreover, the present invention further provides
circuit assembly 50 in an assembled form, as depicted in FIG. 4, in
which chip die 62 has been mated with substrate 70, and exposed to
appropriate conditions to cause fluxing agent 85 to flux the
adjoining surfaces between solder bumps 82 and solder pads 88, to
cause solder bumps 82 to flow for soldering, and to cause underfill
component 90 to be cured into a thermoset composition in solid
form. As such, chip die 62 is electrically interconnected with
substrate 70 through the use of solder bumps 82. Also, chip die 62
is affixed or adhered to substrate 70 through underfill component
90 which is cured into a cured thermoset underfill compound which
is substantially free of residue from fluxing agent 85, since
underfill component 90 and fluxing agent 85 were provided as
distinct components on discrete portions of integrated circuit chip
60, as opposed to being provided in a homogeneous fluxing adhesive
composition.
[0142] FIGS. 5 and 6 depict a further embodiment of the invention,
in which circuit assembly 50a includes integrated circuit chip 60a
having chip die 62 including solder bumps 82 thereon with fluxing
agent 85 disposed on a surface thereof, as set forth in the
embodiment described above with reference to FIGS. 3 and 4. In the
embodiment of FIGS. 5 and 6, however, integrated circuit chip 62a
includes underfill component 90 as a first underfill component, and
further includes a second underfill component 100. As such, gap 55
formed between the chip die 62 and the substrate 70 around solder
bumps 82 is encapsulated with two separate compositions which cure
to provide an underfill encapsulant within gap 55 including both
underfill component 90 and second underfill component 100.
[0143] Second underfill component 100 is a curable composition
which also provides high adhesive strength and low thermal
expansion. In a similar manner as underfill component 90,
thermosetting resin compositions are particularly useful as second
underfill component 100. Accordingly, second underfill component
100 may be any composition as described herein with respect to
underfill component 90. For example, second underfill component 100
desirably includes, broadly, (a) a curable resin component; (b) an
optional inorganic filler component; and (c) a curing agent
component including an anhydride component, a nitrogen-containing
component, such as an amine compound, an amide compound, and/or an
imidazole compound, and/or combinations thereof, as set forth above
with respect to underfill component 90.
[0144] Second underfill component 100 may be the same composition
as underfill component 90 and provided as a distinct layer to the
circuit assembly 50a. Alternatively, second underfill component 100
may be a thermosetting resin composition which is different from
the composition of underfill component 90. As such, circuit
assembly 50a, including underfill component 90 and second underfill
component 100, may include any combination of thermosetting resin
compositions as set forth above. Underfill component 90 and second
underfill component 100 are desirably selected to include
properties corresponding to the surface to which they are adhered
in the circuit assembly 50a. For example, as shown in FIG. 6,
underfill component 90 is adhered to chip die 62. As such,
underfill component 90 may be a thermosetting composition which,
when cured, has a coefficient of thermal expansion which is
compatible with chip die 62. In a similar manner, second underfill
component 100 is adhered between underfill component 90 and
substrate 70. Accordingly, second underfill component 100 may be a
thermosetting composition which, when cured, has a coefficient of
thermal expansion which is compatible with the substrate 70.
[0145] In desirable assemblies, at least one of underfill component
90 and second underfill component 100 includes a reworkable
composition, as described above. For example, underfill component
90 may be provided as an underfill material, while second underfill
component 100 may provided as a separate and discrete component of
a reworkable composition. With both underfill component 90 and
second underfill component 100 present as discrete and separate
components, the strength and thermal expansion properties can be
borne almost exclusively by underfill component 90. As such, second
underfill component 100 can be employed solely for its reworkable
properties and can, therefore, exist as only a thin layer or a
small part of the overall underfill without the need for additional
filler materials for added strength and expansion. Thus, a high
degree of reworkability can be achieved without sacrificing
strength or other physical properties, since the composition of the
second underfill component 100 can be limited to components
necessary to provide the reworkable aspect.
[0146] As seen in FIG. 6, circuit assembly 50a in an assembled form
includes chip die 62 after it has been mated with substrate 70, and
exposed to appropriate conditions to cause fluxing agent 85 to flux
the adjoining surfaces between solder bumps 82 and solder pads 88,
to cause solder bumps 82 to flow for soldering, and to cause
underfill component 90 and second underfill component 100 to cure
into a thermoset composite in solid form. Thus, chip die 62 is
electrically interconnected with substrate 70 through the use of
solder bumps 82, and is affixed or adhered to substrate 70 through
the cured thermoset composite provided through underfill component
90 and second underfill component 100 which are substantially free
of residue from fluxing agent 85. Moreover, underfill component 90
may represent a first dielectric layer which has a coefficient of
thermal expansion which is compatible with chip die 62, while
second underfill component 100 may represent a second dielectric
layer which has a coefficient of thermal expansion which is
compatible with substrate 70.
[0147] Integrated circuit chip 60 may be assembled through
application of the appropriate layers to form the various
components, thus forming an integrated circuit chip having
electrical contacts and one or more underfill components
pre-assembled thereon, which can be effectively soldered and
affixed to a circuit board substrate. Such assembly may be
accomplished by providing chip die 62 with electrical contacts
including solder bumps 82 which are flowable. Solder bumps 82 can
be applied through any known method for solder bump application.
Fluxing agent 85 is applied over at least a portion of solder bumps
82 which are provided for electrical interconnection with substrate
70, and may be applied over the entire surface of solder bumps 82.
Such application may be accomplished by dissolving the fluxing
agent in a suitable solvent system for printing over solder bumps
82, for example by screen printing, stencil printing, jet printing,
pad printing, or offset printing, as noted above. After application
of the solution of fluxing agent 85, the chip die 62 is b-staged by
heating in an oven at a temperature from about
40.degree.-150.degree. C. for a time period of about 5-6 hours,
desirably at a temperature from about 80.degree.-100.degree. C. for
a time period of about 1-3 hours. Such heating results in drying of
the fluxing agent 85 on solder bumps 82 by driving off the solvent
from the solution of the fluxing agent as applied, leaving behind
the fluxing agent in a tackified film having a desirable thickness
of about 0.25-2.0 mils, more desirably about 0.5 to about 1
mil.
[0148] A curable thermosetting composition representing underfill
component 90 is thereafter dispensed in a flowable form on chip die
62 around solder bumps 82. For example, the curable thermosetting
composition as described above may be printed onto chip die 62 at a
predetermined area distinct from fluxing agent 85. As with printing
of fluxing agent 85 onto solder bumps 82, such printing of the
curable thermosetting composition onto chip die 62 may be
accomplished in any known manner, for example, by stencil printing,
jet printing, pad printing, or offset printing. Desirably, a
stencil printing process is performed in which the areas of the
solder bumps 82 are excluded from the printing. As such, the
curable thermosetting composition representing underfill component
90 is printed over the entire surface of chip die 62 except for the
solder bumps 82.
[0149] After dispensing the curable thermosetting composition, the
chip die 62 is again b-staged in a drying oven in a similar manner
and under similar conditions as with drying of the fluxing agent
85. For example, the chip die 62 having the curable thermosetting
composition dispensed thereon in a flowable form is desirably dried
at a temperature from about 60.degree.-100.degree. C. for a time
period of about 1-3 hours. Such heating results in drying of the
curable thermosetting composition on chip die 62 by driving off the
solvent, thereby reducing the flowability of the composition,
leaving underfill component 90 on the chip die 62 as a curable
thermosetting solid residue compound in a tackified form, at a
thickness of about 1 to about 10 mils, more desirably about 3 to
about 4 mils. Integrated circuit chip 60 is thereby provided for
attachment to substrate 70.
[0150] In embodiments including a second underfill component 100, a
second curable thermosetting composition may then be dispensed in a
flowable form on underfill component 90 at a predetermined area
distinct from fluxing agent 85, such as by printing over underfill
component 90 in a similar manner as with underfill component 90.
After dispensing the second curable thermosetting composition, the
chip die 62 coated as such is again b-staged by drying in an oven
in a similar manner and under similar conditions as with drying of
the fluxing agent 85 and underfill component 90 as described above.
As with underfill component 90, such heating results in drying of
the second curable thermosetting composition on bulk underfill
component 90 by driving off the solvent, thereby reducing the
flowability of the composition, leaving second underfill component
100 on underfill component 90 as a second curable thermosetting
solid residue compound in a tackified form, having a thickness of
about 0.5 to about 5 mils, more desirably about 1 to about 2
mils.
[0151] As shown in FIGS. 3 and 5, a portion of solder bumps 82,
including fluxing agent 85 coated thereover, is exposed from
underfill component 90 and, when included, from second underfill
component 100. This is preferably achieved by direct printing of
the underfill component 90 and the second underfill component 100
at predetermined areas around the solder bumps 82. As such, solder
bumps 82 protrude beyond the underfill materials. In an alternate
embodiment, solder bumps 82 may be covered by the underfill
component 90 and/or the second underfill component 100 during
printing, after which the portion of the underfill component 90
and/or the second underfill component 100 covering solder bumps 82
is ground away, melted away, shaved off, or otherwise removed to
expose the solder bumps prior to attachment to the substrate. In
procedures in which the underfill component 90 and/or the second
underfill component 100 include a reworkable composition, any
melting away of the underfill from solder bumps 82 should occur
prior to the b-stage drying of the appropriate layer including the
reworkable composition, while solvent is still present within the
reworkable composition.
[0152] To assemble circuit assembly 50, the integrated circuit chip
60 is mated with the substrate 70 to form a mated assembly, with
chip die 62 positioned so that solder bumps 82 are facing substrate
70 and aligned with the solder pads 88 of substrate 70, as depicted
in FIG. 2. Integrated circuit chip 60, including chip die 62 having
solder bumps 82 and underfill component 90, is moved into intimate
contact with the substrate 70, such that solder bumps 82 with
fluxing agent 85 coated thereon are in contacting relation with
solder pads 88. The assembly is then exposed to temperature
conditions sufficient to promote electrical interconnection between
integrated circuit chip 60 and substrate 70, for example, by
heating to a temperature capable of causing reflow of the solder,
using any known heating and reflow techniques. Such heating causes
fluxing agent 85 to become activated, reducing the oxides on the
solder bumps 82 and the solder pads 88, and permitting alloying of
the solder bumps 82 to the solder pads 88. During the heating in
this reflow process, underfill component 90 is cured to a solid
form. Thus, reflow of solder bumps 82 and curing of underfill
component 90 and reworkable component 100 occur within the same
processing procedure. As such, circuit assembly 50 is formed with
the circuitry encapsulated by underfill component 90 as depicted in
FIG. 4, with a continuous seal provided around the periphery of the
assembly to protect the surface from environmental contamination. A
semiconductor device is thus provided for various electronic
applications.
[0153] Circuit assembly 50a of FIG. 6 is assembled in a similar
manner, with integrated circuit chip 60a provided for attachment to
substrate 70. In such an embodiment, curing of underfill component
90 and second underfill component 100 occur within the same
processing procedure.
[0154] The solder reflow profile may be composed of several zones,
where a temperature is reached or maintained for a set time period,
or temperature increases occur over a set time period. For example,
such zones may be referred to as a pre-heating zone, a soaking zone
and a reflow zone. In the pre-heating zone, the mated assembly is
gradually heated to the soaking zone temperature. The heating
gradation in the pre-heating zone may progress through the
temperature range of 30.degree. C. to 130.degree. C. in a period of
time of up to 60 seconds. In the soaking zone, the mated assembly
is allowed to thermally equilibrate so that the thermal expansions
of the various components may occur and temperature adjustments can
occur. During initial heating in the soaking zone, the temperature
is increased above a temperature at which the fluxing agent is
activated to clean the metal surfaces, for allowing the solder to
eventually make secure electrical interconnection when exposed to
elevated temperatures reached during the reflow zone. The heating
gradation in the soaking zone may progress through the temperature
range of 150.degree. C. to slightly greater than 180.degree. C.,
such as 183.degree. C., from a period of time of 60 to 175 seconds
from initiation. In the pre-heating and soaking zones, it is
desirable for the underfill composition to remain ungelled.
[0155] In the reflow zone, the solder melts, thereby flowing and
forming the electrical connection. The underfill composition should
gel after the solder has flowed and forms the electrical
connection; otherwise, the component present can shift, thereby
causing an electrical disconnect. The heating gradation in the
reflow zone may progress through the temperature range of slightly
greater than 180.degree. C., such as about 183.degree. C., to about
220.degree. C..+-.10.degree. C., from a period of 175 to 205-265
seconds from initiation. It is desirable for the underfill
composition to cure completely after the solder has flowed to form
the electrical connection. Curing of the underfill composition
establishes an electrical interconnection while encapsulating the
semiconductor device onto the substrate.
[0156] As noted above, embodiments including a reworkable
composition within underfill component 90 and/or second underfill
component 100 provides circuit assembly 50 with a cleavable linkage
which allows for repair, replacement, recovery and/or recycling of
operative components from assemblies that have become at least in
part inoperative. Removal of integrated circuit chip 60 from
substrate 70 can therefore be accomplished by heating the thermoset
underfill component including the reworkable composition to a
temperature above its cure temperature, causing the composition to
thermally degrade. For example, the area around the integrated
circuit chip 6, which is to be removed is heated to a temperature
above the cure temperature of the resin composition for a
sufficient time period to allow the resin composition to soften.
Although no particular limitation is placed on the way in which
heating occurs, localized heating is particularly desirable, such
as the application of hot air to the failure site by a heating gun.
Such heating results in melting of the solder of solder bumps 82,
and softening of the resin of the reworkable composition by partial
decomposition, thereby causing a reduction in bond strength. The
integrated circuit chip 60 can then be removed from the substrate
70, such as with tweezers or a pair of pliers.
[0157] After the integrated circuit chip 60 is removed from
substrate 70, a residue of the cured reaction product of the
underfill composition and a residue of the solder are left on the
circuit board substrate 70. The residue of the cured product of the
underfill composition can be removed, for example, by scraping it
off after the residue has been softened by heating it to a
predetermined temperature. The residue of the solder can be
removed, for example, by use of a solder-absorbing braided
wire.
[0158] A new integrated circuit chip can then be mounted onto the
circuit board substrate, in the manner as described above.
[0159] By providing the fluxing agent as a separate and distinct
component from the adhesive underfill materials, the fluxing agent
can be used at a high concentration, such as a highly concentrated
organic acid. Since it is provided as a separate, discrete
component, the fluxing agent can act effectively for its purpose as
a fluxing agent for providing fluxing action for the soldering
operation, and will not deleteriously affect the strength and
adhesion properties of the underfill material, as is oftentimes the
case in homogeneous fluxing underfill adhesives which incorporate
the fluxing agent and underfill material in a single
composition.
[0160] Moreover, in embodiments in which one of the underfill
compositions includes a reworkable composition as a discrete and
separate component or layer, high strength resins can be used in
combination with low expansion fillers for the bulk underfill
component. Thus, the bulk underfill layer provides excellent
physical strength with low overall thermal expansion, without any
deleterious effects on the fluxing activity of the fluxing agent or
any sacrifice in performance due to incorporation of a reworkable
composition therein. Also, since the reworkable component is
contained in only a thin layer directly at the surface of
attachment of the circuit chip to the substrate, a high degree of
reworkability can be achieved directly at the bonding point without
sacrificing strength and fluxing activity, as may occur in
assemblies which incorporate reworkable resin compositions into the
bulk adhesive underfill.
[0161] In a further embodiment shown in FIG. 7, integrated circuit
chip 60b is provided with solder bumps 82 pre-assembled thereon and
pre-coated with a multi-layer structure prior to assembly to the
substrate 70. The multi-layer structure includes separate layers,
each of which perform distinct functions. For example, chip die 62
may include a first layer which is a stress absorbing layer 110,
attached directly to surface 64 of chip die 62. Underfill component
90 is provided thereover as a separate layer, in a manner and
arrangement as discussed above. In such an arrangement, the use of
the additional stress absorbing layer 110 provides for a circuit
assembly 50b having improved strength. In a similar manner, such a
stress absorbing layer 110 can be provided in an embodiment
including both an underfill component 90 and a second underfll
component 100, providing an integrated circuit chip 60c, as shown
in FIG. 8. In such an embodiment, underfill component 90 and second
underfill component 100 are provided over stress absorbing layer
110 as separate layers, in a manner and arrangement as discussed
above, thereby providing a circuit assembly 50c having improved
strength.
[0162] It is noted that chip die 62 as discussed herein may be
provided as an individual chip die, or may be provided as a chip
scale package. Accordingly, in yet a further embodiment shown in
FIG. 9, a circuit assembly 150 is provided including a chip scale
package 160. Chip scale packages are known in the art for use in
electrical connections of circuits with circuit board substrates.
In the present embodiment, circuit assembly 150 includes a
structure similar to that shown in the embodiment depicted in FIG.
4, except that chip die 62 is replaced with chip scale package 160.
For example, circuit assembly 150 includes a circuit board
substrate 70 including solder pads 88 thereon. Substrate 70,
however, is not attached directly to an integrated circuit chip, as
in the embodiment depicted in FIG. 4, but is instead attached to
chip scale package 160, which may include, for example, a chip die
attached to a separate carrier substrate or an interposer layer, as
is known in the art. In such an embodiment, solder bumps 82 may be
provided on such a separate carrier substrate or on the interposer
layer, in a similar manner as set forth with respect to circuit
chip 60 in the previous description. Moreover, chip scale package
160 is attached to substrate 70 in a similar manner as with the
previous description, through fluxing agent 85 coated over solder
bumps 82, and underfill component 90. Such a chip scale package 160
can also be assembled to substrate 70 through a first underfill
component and a second underfill component, as shown in circuit
assembly 150a in FIG. 10.
[0163] The present invention will be more readily appreciated with
reference to the examples which follow.
EXAMPLES
Example I
Fluxing Agent
[0164] A fluxing agent was prepared in accordance with the present
invention including the following components:
1 TABLE I COMPONENT WEIGHT PERCENT Fluxing agent (diacid).sup.1 50
Epoxy resin.sup.2 25 Carrier solvent 25 (ethyl
ethoxypropionate).sup.3 .sup.1Commercially available as DIACID 1550
from Westvac Oleo Chemicals. .sup.2Commercially available as DER
661 from Dow Chemical Co. .sup.3Commercially available as EEP from
Eastman.
[0165] The fluxing agent prepared including the above components
exhibits excellent storage stability, with a shelf life of
.gtoreq.4 months. Further, upon b-staging, the fluxing agent dries
to a tacky solid material. During use in solder reflow techniques,
the fluxing agent exhibits excellent fluxing activity.
Example II
Bulk Underfill Composition
[0166] A bulk underfill composition according to the present
invention may be prepared including the components as set forth in
Table II-A:
2TABLE II-A COMPONENT WEIGHT PERCENT Epoxy resin (bisphenol A
type).sup.1 5-25 Epoxy resin (novalec type).sup.2 5-25 Curing agent
(dicyandiamide).sup.3 0.1-10 Pigment (carbon black) 0-1 Structural
filler (spherical silica).sup.4 0-80 Surfactant.sup.5 0-2 Adhesion
promoter (silane).sup.6 0-5 Viscosity/thixotropy modifier (fused
silica).sup.7 0-5 Carrier solvent (ethyl ethoxy propionate).sup.8
2-40 .sup.1Commercially available as EPON 1001 from Shell Chemical
Co. .sup.2Commercially available as XD-1000-2L from Nippon Kayaku.
.sup.3Commercially available as CG 1400 from Air Products.
.sup.4Commercially available as ML-801 from Tokuyama Corp.
.sup.5Commercially available as BYK-555 from BYK-Chemie,
Wallingford, CT. .sup.6Commercially available as A-1100 from Witco
Corp. .sup.7Commercially available as AEROSIL R812S from Degussa.
.sup.8Commercially available as EEP from Eastman.
[0167] A specific formulation was prepared according to the
following components as set forth in Table II-B:
3TABLE II-B COMPONENT WEIGHT PERCENT Epoxy resin (bisphenol A
type).sup.1 12.44 Epoxy resin (novalec type).sup.2 12.44 Curing
agent (dicyandiamide).sup.3 1.49 Pigment (carbon black) 0.1
Structural filler (spherical silica).sup.4 62.05 Surfactant.sup.5
0.1 Adhesion promoter (silane).sup.6 0.4 Viscosity/thixotropy
modifier (fused silica).sup.7 1.47 Carrier solvent (ethyl ethoxy
propionate).sup.8 9.51 .sup.1Commercially available as EPON 1001
from Shell Chemical Co. .sup.2Commercially available as XD-1000-2L
from Nippon Kayaku. .sup.3Commercially available as CG 1400 from
Air Products. .sup.4Commercially available as ML-801 from Tokuyama
Corp. .sup.5Commercially available as BYK-555 from BYK-Chemie,
Wallingford, CT. .sup.6Commercially available as A-1100 from Witco
Corp. .sup.7Commercially available as AEROSIL R812S from Degussa.
.sup.8Commercially available as EEP from Eastman.
[0168] The bulk underfill composition prepared including the above
components exhibits adhesion characteristics, particularly when
used in connection with multilayered electronic assemblies of the
present invention. In solder reflow techniques, the bulk underfill
composition cures to provide an excellent stress reinforcement.
Example III
Reworkable Composition
[0169] Six epoxy resin compositions were prepared as follows:
4TABLE III-A Ratio of epoxy resin components Epoxy Epoxy Epoxy
Epoxy Epoxy Epoxy Epoxy resin component A B C D E F Bisphenol
A-type epoxy.sup.1 1 2 4 2 2 0 Novalec type epoxy.sup.2 1 2 2 4 0 2
Reworkable epoxy.sup.3 1 1 3 3 1 1 .sup.1 Commercially available as
EPON 1001 F from Shell Chemical Co. .sup.2 Commercially available
as XD-100-2L from Nippon Kayaku. .sup.3 Reworkable epoxy
composition based on one or more epoxies having thermally cleavable
linkages.
[0170] Reworkable compositions can be prepared including each of
these Epoxy Resins A-F, having the following components:
5TABLE III-B COMPONENT WEIGHT PERCENT Epoxy resin A-F from Table
III 10-50 Curing agent (dicyandiamide).sup.1 0.1-10 Structural
filler (spherical silica).sup.2 0-80 Surfactant.sup.3 0-2 Adhesion
promoter (silane).sup.4 0-5 Viscosity/thixotropy modifier (fused
silica).sup.5 0-5 Carrier solvent (ethyl ethoxy propionate).sup.6
2-40 .sup.1Commercially available as CG 1400 from Air Products
Corp. .sup.2Commercially available as ML-801 from Tokuyama.
.sup.3Commercially available as BYK-555 from BYK Corp.
.sup.4Commercially available as A-1100 from Witco Corp.
.sup.5Commercially available as AEROSIL R812S from Degussa.
.sup.6Commercially available as EEP from Eastman.
[0171] Six specific reworkable compositions were prepared from the
six Epoxy Resins A-F as shown in Table III-A to produce
Compositions A-F, including the following components:
6TABLE III-C COMPONENT WEIGHT PERCENT Epoxy resin A-F from Table
III 24.88 Curing agent (dicyandiamide).sup.1 1.49 Structural filler
(spherical silica).sup.2 62.05 Surfactant.sup.3 0.1 Adhesion
promoter (silane).sup.4 0.4 Viscosity/thixotropy modifier (fused
silica).sup.5 1.47 Carrier solvent (ethyl ethoxy propionate).sup.6
9.61 .sup.1Commercially available as CG 1400 from Air Products
Corp. .sup.2Commercially available as ML-801 from Tokuyama.
.sup.3Commercially available as BYK-555 from BYK Corp.
.sup.4Commercially available as A-1100 from Witco Corp.
.sup.5Commercially available as AEROSIL R812S from Degussa.
.sup.6Commercially available as EEP from Eastman.
[0172] The bulk underfill compositions prepared including the above
components exhibit excellent properties for use in connection with
multilayered electronic assemblies of the present invention. In
solder reflow techniques, the bulk underfill compositions cure to
provide excellent adhesion to substrate surfaces. Upon heating of
the compositions to a temperature above the solder reflow
temperature and above the cure temperature, such as about
270.degree. C., the reworkable compositions soften and degrade,
thereby providing reworkability characteristics appropriate for use
in multilayered electronic assemblies.
Example IV
[0173] Each of Compositions A-F from Example III were evaluated for
adhesion performance after curing thereof. In particular, six
separate test die were mounted to fiberglass circuit board
substrates with a small amount of each of Compositions A-F applied
as an adhesive. Each substrate was then heated by subjecting it to
a maximum reflow temperature of 230.degree. C., resulting in curing
of Compositions A-F during such heating. After such curing, die
shear strength of each the compositions was tested by shearing off
the test die on a Dage-4000 shear test instrument. The results of
this testing are shown in Table IV:
7TABLE IV COMPOSITION Kg force/square mm psi A 3.3 4634.9 B NT* NT*
C 1.9 2704.5 D 3.3 4633.1 E 1.0 1455.3 F 2.9 4078.6 *Not
Tested.
[0174] As is apparent from the die shear strengths shown in Table
IV, each of the Compositions A-F prepared as reworkable components
in accordance with the present invention demonstrate acceptable
strengths for substrate adhesion, with specific formulations
achieving excellent die shear strengths after curing.
Example V
[0175] In Example V, each of Compositions A-F were evaluated to
determine cleanability of the reworkable compositions.
[0176] Each of reworkable compositions A-F were stencil printed
onto a fiberglass circuit board substrate and b-staged to achieve
dryness at 70.degree. C. for a period of 2 hours. After curing each
of Compositions A-F, each circuit chip was subjected to a rework
temperature of 270.degree. C. At such temperature, each of
Compositions A-F softened allowing for removal of the circuit chip
from the circuit board substrate. Each substrate was subjected to
mechanical brushing of the surface in order to remove the residue
remaining of the reworkable composition. Table V demonstrates the
cleaning time after temperature exposure for periods of one and
three minutes for each of Compositions A-F:
8TABLE V EXPOSURE AT 270.degree. C. CLEANING TIME COMPOSITION
(minutes) (minutes) A 1 3-3.5 A 3 3-3.5 B 1 4.5 B 3 5.0 C 1 3-4.5 C
3 2.0 D 1 4.5 D 3 2.0-5.0 E 1 2.5-3.0 E 3 3.5 F 1 3.5-5.0 F 3
3.5-4.0
[0177] As can be seen from the results shown in Table V, each of
Compositions A-F demonstrates excellent cleanability after rework
of the composition.
Example VI
[0178] Example VI demonstrates adhesion of reworkable compositions
in accordance with the present invention after multiple high
temperature reflow cycles.
[0179] Composition A from Example III above was applied to a
substrate and b-staged for drying. The substrate including
Composition A thereon was then subjected to multiple reflow cycles
with a peak reflow temperature of 230.degree. C. for a period of
two minutes during each reflow cycle. After one reflow cycle,
Composition A demonstrated 84.4 percent residual adhesion to the
substrate. After a second reflow cycle, Composition A demonstrated
96.1 percent residual adhesion. After a third reflow cycle,
Composition A demonstrated slightly reduced adhesion at 92.9
percent residual adhesion. Even after six reflow cycles,
Composition A demonstrated 88.6 percent residual adhesion to the
substrate. Such results demonstrate the excellent adhesion
demonstrated by the compositions used to assemble the inventive
integrated circuit chips and structures assembled therewith.
Example VII
[0180] A fluxing agent prepared in accordance with the formulation
of Example I may be applied to solder bumps on circuit chips
constructed of silicon by stencil printing. The fluxing agent can
b-staged for drying of the fluxing agent. A bulk underfill
composition according to Example II may then be stencil printed on
the circuit chips around the solder bumps including the fluxing
agent coated thereon. The chips are again b-staged to dry the bulk
underfill component in a similar manner as with the fluxing agent.
Each of reworkable Compositions A-F can then be stencil printed
onto individual circuit chips over the bulk underfill component
around the solder bumps. Again, b-stage drying of each of the
circuit chips to dry the reworkable component may be accomplished
in a similar manner as with the fluxing agent and the bulk
underfill component.
[0181] After such application, each chip can be applied to a
substrate, and solder reflowed at a temperature of 230.degree. C.
for a period of about 2 minutes, resulting in reflowing of the
solder and curing of the bulk underfill composition and the
reworkable composition.
[0182] Circuit assemblies produced in such a manner provide
excellent electrical connection between the chip and the circuit
board. Additionally, as observed in earlier examples, excellent
adhesion of the chip to the circuit board can be achieved. Further,
reworkability of the chip can be accomplished by subjecting the
assembly to rework temperatures of about 270.degree. C. Upon such
reworking, the chips can be readily removed, with little mechanical
brushing required to remove residue from the circuit board
substrate surface.
[0183] The invention being thus described, it will be evident to
those skilled in the art that the same may be varied in many ways.
Such variations are not to be regarded as a departure from the
spirit and scope of the invention and all such modifications are
intended to be included within the scope of the claims.
* * * * *